Oracle RMAN backup is taking too long to initiate child sessions

Hi ,

we have been using Netbackup 7.5.0.6 as master server and oracle RMAN backup for one of the DB's is taking too long to initiate the child sessions. One hour interval is between the child sessions. I can see the data being pumped at 31 mbps to the media server which is supposed to be good speed when the child sessions get initiated in parallel.But , As child sessions are too long to initiate , its been a big concern for us on the time to backup the data.